As solid-state imaging devices (image sensors) using photoelectric conversion elements which detect light to generate electric charges, CMOS (complementary metal oxide semiconductor) image sensors have been put into practical use. CMOS image sensors are being widely applied as parts of digital cameras, video cameras, monitoring cameras, medical endoscopes, personal computers (PC), mobile phones, and other portable terminal devices (mobile devices) and various other types of electronic apparatuses.
A CMOS image sensor has a floating diffusion (FD) amplifier having, for each pixel, a photodiode (photoelectric conversion element) and floating diffusion layer. For readout, the mainstream type is the column parallel output type that performs selects a certain row in a pixel array and simultaneously reads the pixels out to a column output direction.
In this regard, in a CMOS image sensor, photo charges which are generated and accumulated (stored or integrated) in the photodiodes are sequentially scanned and read out for each of the pixels or each of the rows. When performing this sequential scanning, that is when employing a rolling shutter as an electronic shutter, the start times and end times of exposure for accumulating photo charges cannot be made to match in all of the pixels. For this reason, in the case of sequential scanning, there is the problem of occurrence of distortion in a captured image when capturing an image of a moving subject.
Therefore, in capturing an image of a subject moving at a high speed or in sensing applications requiring simultaneity of the captured image, where image distortion is not allowed, as the electronic shutter, a global shutter which starts the exposure and ends the exposure at the same timing for all pixels in the pixel array portion is employed.
In a CMOS image sensor employing a global shutter as the electronic shutter, a pixel is, for example, provided is made of a signal holding part which holds a signal read out from a photoelectric conversion reading part in a signal holding capacitor. In a CMOS image sensor employing a global shutter, simultaneity of an entire image is secured by accumulating the charges of the photodiodes as voltage signals all together in the signal holding capacitors in the signal holding parts and later sequentially reading them out (see for example NPLT 1). Further, this CMOS image sensor has bypass switches for bypassing the signal holding parts and transferring the outputs of the photoelectric conversion reading parts to signal lines and therefore is configured so as to have a rolling shutter function together in addition to a global shutter function.
The stacked type CMOS image sensor disclosed in NPLT 1 has a stacked structure of a first substrate (pixel die) and a second substrate (ASIC die) connected through microbumps (connecting parts). Further, the photoelectric conversion reading parts of the pixels are formed on the first substrate, while the signal holding parts of the pixels, signal lines, vertical scanning circuit, horizontal scanning circuit, column readout circuit, and so on are formed on the second substrate.